Implant system

ABSTRACT

The invention relates to an implant system having at least one shaft of a prosthesis, in particular a hip joint prosthesis, which can be anchored without cement, and a set of instruments for the preparation of the bone in which the shaft is to be anchored, wherein the shaft has an arcuate base body with a trapezoidal or rectangular cross-section and the set of instruments includes a first instrument which is shaped in accordance with the arcuate shape of the shaft and with which a recess serving for the reception of the base body can be established in the bone; and wherein the shaft is provided with ribs in the proximal region and the set of instruments includes a guide body shaped in accordance with the arcuate shape of the shaft for a second instrument with which structures can be manufactured in the bone serving to fix a path for the shaft ribs when the guide body is located in the recess.

The invention relates to an implant system having at least one shaft ofa prosthesis, in particular a hip joint prosthesis, which can beanchored without cement, and a set of instruments for the preparation ofthe bone in which the shaft is to be anchored.

A shaft of a hip joint prosthesis which can be anchored without cementis known from EP 0 135 755 A1. This prosthesis shaft is straight, has atrapezoidal cross-section and has groove-like recesses in the proximalregion. The rib structure formed hereby is intended to improve theabsorption of torsional forces in the proximal shaft region.

It is a problem on the insertion of straight shafts that the trochantermajor of the femur can hereby be impaired. When curved shafts are used,in contrast, the trochanter can admittedly be maintained. However, theinsertion of a curved shaft is again a problem if the shafts should haverib structures such as were mentioned above.

The reason for this is that the shaft can reach a pre-determined endposition in the bone when hammered on a plurality of different movementpaths. This is not a problem as long as the shaft has no rib structures.However, if the shaft is provided with rib structures, there is a riskthat the ribs cut their own track into the bone which allows the shaftto move onto an incorrect path on which the shaft cannot be driven intothe end position, at least no longer in the desired manner.

Due to these problems occurring on the insertion, curved shafts providedwith ribs have not become as widespread as would have been expected dueto the existing advantages per se of such shafts.

It is the object of the invention to provide an implant system withwhich curved prosthesis shafts can also be reliably anchored in the bonein a simple and reliable manner.

This object is satisfied by the features of claim 1 and in particular inthat the shaft has an arcuate base body and the set of instrumentsincludes a first instrument which is shaped in accordance with thearcuate shape of the shaft and with which a recess serving for thereception of the base body can be established in the bone, and whereinthe shaft is provided with ribs in the proximal region and the set ofinstruments includes a guide body for a second instrument which isshaped in accordance with the arcuate shape of the shaft and with whichsecond instrument structures can be established in the bone serving forthe fixing of a path for the shaft ribs when the guide body is locatedin the recess.

In accordance with the invention, in addition to the instrument, inparticular a rasp, serving for the establishment of the recess for thebase body, a further instrument is provided with which the bone can bedirectly prepared for the guidance of the shaft ribs. The invention ischaracterized in that the recess previously established by means of thefirst instrument is used for the working to be carried out by the secondinstrument in that a guide body is used which is likewise shaped inaccordance with the base body of the shaft, is inserted into the recessand then serves as a guidance for the second instrument. A path issubsequently fixed for the shaft ribs, and thus for the shaft overall,by means of the second instrument guided in a defined manner, said shaftsubsequently being hammered to the bone working taking place by means ofthe second instrument.

Since a guide body corresponding to the shaft with respect to thearcuate form serves as a reference for the working movement of thesecond instrument, it can be ensured in accordance with the inventionthat a track is established for the shaft ribs and thus a path ispre-determined which is adapted to the arcuate shape of the base body ofthe shaft. It is hereby ensured that the curved shaft provided with theribs moves in the desired manner into the end position previouslypre-determined by means of the first instrument.

The ribs or the tangents at the ribs extend in accordance with the shaftcurvature at an angle to the shaft axis different from zero. This ribangle in particular lies in the range from 0° to 45°, with, however,larger angles also being possible, and is selected in dependence on thearcuate shape of the shaft.

The guide body can be provided in the form of a separate part.Alternatively, the first instrument can simultaneously be made as theguide body for the second instrument. In this case, an additional guidebody can be dispensed with.

Further preferred embodiments of the invention are also recited in thedependent claims, in the description and in the drawing.

Provision is thus preferably made for the cross-section of the shaft tobe rectangular or trapezoidal with pronounced longitudinal edges whichestablish the contact to the cortex. Provision is preferably furthermoremade for the arcuate shape of the base body to be selected in particularwith respect to curvature and length in relation to two oppositelydisposed edges, i.e. a lateral edge and a medial edge, such that an endposition of the base body results which is clearly defined by aplurality of contact positions, in particular three contact positions,at the cortex of the bone. It is hereby ensured that the respective basebody centers itself on insertion in accordance with its rectangular ortrapezoidal cross-section and that hollow spaces are no longer presentbetween the base body and the bone bed formed by the cortex in the endposition since a clamping also takes place between the base body and thebone bed formed by the two lateral edges and between the two medialedges. The curvature of the base body and the length of the base bodyand/or of the shaft are in particular matched to one another in apre-determined manner.

It is particularly advantageous if, in accordance with a furtherembodiment of the invention, the extent of the shaft ribs is adapted tothe arcuate shape of the base body of the shaft such that an endposition of the base body clearly defined by a plurality of contactpositions, in particular three contact positions, at the cortex of thebone can be reached between oppositely disposed lateral and medialedges. Provision is made for the contact positions not to be punctual,but to be formed in the form of zones stretched in the longitudinaldirection.

The ribs of the shaft can extend in both a straight and in a curvedmanner. In this process, it is not compulsory for all ribs to bestraight or for all ribs to be curved. Both straight and curved ribs canbe provided within a rib structure including a plurality of ribs. It isbasically also possible to provide only one single rib on each side ofthe shaft. It is furthermore possible that one or more ribs are onlyprovided on one side.

The extent of the ribs can in particular be made dependent on theirrespective length. In this process, ribs not exceeding a specific lengthcan be made straight, whereas ribs exceeding a specific length canextend in a curved manner.

Provision is furthermore preferably made for the shaft ribs to extendtoward distal starting from an at least approximately common plane. Thiscommon plane is preferably disposed in the region of a resection planeof the bone with an inserted shaft.

If both straight and curved shaft ribs are present, provision ispreferably made in accordance with a further embodiment of the inventionfor the straight shaft ribs, on the one hand, and tangents at the curvedshaft ribs, on the other hand, to extend to the shaft axis at the sameangle different from zero.

Provision can in particular be made with a relatively long shaft for itsbase body to be provided with a flattened area at its lateral side inthe region of its distal end. This preferably also applies to the firstinstrument and to the guide body. The observation of an optimum path onthe hammering in of the shaft or on the insertion of the firstinstrument and of the guide body is hereby facilitated. The distal tipcan in each case be displaced asymmetrically toward medial.

It is furthermore proposed that the first instrument is provided with arespective chamfer at the anterior and posterior sides.

Provision can furthermore be made for the distal end of the firstinstrument to project in the distal direction beyond a base body of thefirst instrument corresponding to the base body of the shaft. The firstinstrument is hereby provided with a distal extension in comparison withthe shaft.

The second instrument, with which the structures serving for the fixingof a path for the shaft ribs are established in the bone, is preferablymovable toward distal along a guide path pre-determined by the guidebody. This guide path and the shaft ribs are adapted to one another withrespect to their extent so that the shaft ribs run in their own,pre-determined track on the hammering in of the shaft. The guide path ispreferably curved in accordance with shaft ribs extending in a curvedmanner.

The guide provided at the guide body for the second instrument isfurthermore preferably made as a compulsory guide in full or regionally.

Provision is furthermore preferably made for the second instrument to beU-shaped or fork-shaped and for it to be pushable onto the guide bodywith the free ends of the U arms or fork arms at the front.

It is furthermore proposed in accordance with the invention that thesecond instrument is provided on its front side and/or rear side with anumber of working webs corresponding to the number of shaft ribs. Theworking webs are matched to the geometry of the shaft ribs and arepreferably made in each case as chisels or rasps.

Consequently, an at least partial negative of the shaft region providedwith the ribs can be established using the second instrument, wherebythe ribs are forced onto the correct path right from the start on thehammering in of the shaft.

The working webs can each be shorter and/or lower than the correspondingshaft ribs. The track length which can hereby be established independence on the length of the guide formed at that guide body for thesecond instrument is sufficient for a clear track formation in the bone.

Provision is furthermore preferably made for all working webs to have atleast substantially the same length.

The invention will be described in the following by way of example withreference to the drawing. There are shown:

FIG. 1 different views of a shaft in accordance with an embodiment ofthe invention;

FIG. 2 different views of a first tool in accordance with an embodimentof the invention made as a rasp;

FIG. 3 different views of a guide body and of a second tool inaccordance with an embodiment of the invention couplable to the guidebody and made as a chisel or as a rasp;

FIG. 4 the guide body and the second tool of FIG. 3 in the coupled statein different relative positions; and

FIG. 5 a cross-section in the curved proximal part of the shaft of FIG.1 in an enlarged representation.

The shaft 11 of a hip joint prosthesis in accordance with the inventionshown in FIG. 1 has a base body 17 curved in arcuate shape, a neck 33and a coupling section 35 for a head of a prosthesis (not shown). Thearcuate shape of the base body 17 is of a design opening conically inthe direction of the axis of the neck.

The base body 17 has a rectangular or trapezoidal cross-section withpronounced edges in its longitudinal direction.

Four respective ribs 19 extending in parallel and of different lengthare applied in the proximal region of the base body 17 on the front sideand on the rear side of the shaft 11 and extend toward distal startingfrom an approximately common plane. This plane is selected such that itlies in the region of the resection plane of the bone with the shaft 11inserted in the bone (not shown).

Starting from this plane, the ribs 19 each extend in a straight manner,with in each case a slightly curved rib section with a constant radiusof curvature adjoining with the longer ribs 19, with the respectiveproximal straight rib section coinciding with the tangent at the curvedrib section.

The straight rib sections and thus the tangents at the curved ribsections extend toward the shaft axis A at an angle α different to zero.

The height of the ribs 19 reduces toward distal. As can in particular beseen from the lower representation in FIG. 1, the ribs 19 each have arectangular base with a top triangle in cross-section, i.e. the ribs 19extend upwardly to a tip.

The arcuate shape of the base body 17 is selected such that therespectively oppositely disposed lateral and medial edges of the basebody 17 lie on the cortex of the bone forming the bone bed for the basebody 17 at three contact positions 21 at the desired end position of theshaft 11 in the bone. This ensures that the base body 17 always wedgesin the same end position in the bone at which there are no longer anyhollow spaces present between the base body 17 and the bone bed and thebase body 17 centers itself on the hammering in of the shaft 11.

In the region of its distal end, the base body 17 is provided at itslateral side with a flattened area 25. The hammering in of the shaft 11along the desired path is hereby facilitated.

The rasp 13 in accordance with the invention shown in FIG. 2 forming thefirst instrument in the sense of the invention is characterized in thatit has a base body 17′ which corresponds to the base body 17 of theshaft 11 with respect to the arcuate shape. The rasp 13 serves toprepare the medullary cavity of the bone and/or the cortex such that theshaft 11 can be wedged in the desired end position by being hammered in.

The distal end of the rasp 13 projects beyond the base body 17′ in thedistal direction and forms a tip which is provide with a respectivechamfer 26 on the ventral and dorsal sides to take account of thecurvature of the femoral bone and to permit the use of the instrumentfor the left femur and for the right femur. In this process, the tip ofthe rasp is orientated more to medial to be able to be centered betterduring the whole lowering procedure.

The guide body 14 in accordance with the invention shown in FIG. 3 isalso adapted to the shaft 11 to the extent that it has a base body 17″which corresponds to the base body 17 of the shaft 11 with respect tothe arcuate shape. The end positions of the shaft 11 and of the guidebody 14 are hereby identical so that the second instrument 15, which islikewise shown in FIG. 3 and which will be looked at in more detail inthe following, can be guided along the guide body 14 such thatstructures are hereby established in the bone where subsequently theshaft 11 is guided by its ribs 19 on the hammering in.

Consequently, a path can be pre-determined for the shaft ribs 19 in thebone by means of the guide body 14 and of the second instrument 15guided at the guide body 14, with the base body 17 of the shaft 11moving into the desired end position on said path.

In the embodiment shown, the guide body 14 is provided at its front sideand at its rear side with recessed flat sides 37 which are bounded byside walls serving as guide surfaces 27. The curvature of the guidesurfaces 27 is selected in accordance with the curvature of the shaftribs 19 such that the shaft ribs 19 run in their own track on thehammering in of the shaft 11.

The second instrument 15 is made in U shape or in fork shape andincludes two arms 29 connected to one another by a coupling section 39,with the spacing between the arms 29 being selected in accordance withthe thickness of the guide body 14 in the region of the flat sides 37.

As FIG. 4 shows, the second instrument 15 can be pressed onto theproximal region of the guide body 14 provided with the flat sides 37 andcan be pushed along the guide body 14 like a slide, and indeed on a pathwhich is pre-determined by the guide surfaces 27 cooperating withcorresponding counter-surfaces 41 of the second instrument 15 (FIG. 3).

The guide arms 29 of the second instrument 15 are provided at theiroutsides with working webs 31 formed in each case as chisels or asrasps. The working webs 31 are arranged in accordance with the ribs 19of the of the shaft 11, with the curvature of the working webs 31moreover corresponding to the curvature of the shaft ribs 19.

In a surgical procedure carried out by means of the implant system inaccordance with the invention, as was explained above, a recess servingfor the reception of the shaft 11 (FIG. 1) is first established in thebone using the rasp 13 (FIG. 2) in that the medullary cavity and thecortex are worked accordingly. Due to the arcuate shape provided for theimplant system in accordance with the invention, the trochanter major ofthe femur is not impaired, since the preparation and the anchoring takeplace through the resection surfaces of the start of the neck of thebone.

Subsequently, after removal of the rasp 13, the guide body 14 (FIG. 3)is inserted into the recess previously established by means of the rasp13. In this process, the base body 17″ of the guide body 14 whichcorresponds to the base body 17 of the shaft 11 with respect to itsarcuate shape is brought into the same end position as later the shaft11.

The second instrument 15 (FIG. 3) is then placed onto the compulsoryguide formed on the guide body 14 by the guide surfaces 27. By movingthe second instrument 15 relative to the guide body 14 along the pathpre-determined by the compulsory guide, tracks are established in thebone for the ribs 19 by means of the working webs 31.

After removal of the guide body 14 and of the second instrument 15, theshaft 11 is finally hammered in. In this process, the shaft ribs 19 runin the tracks which have previously been established by means of thesecond instrument 15 and which force the shaft 11 onto a secure path onwhich the shaft 11 reaches its end position previously pre-determined bymeans of the rasp 13 guided by the ribs 19 in the desired manner.

REFERENCE NUMERAL LIST

-   11 shaft-   13 first instrument, rasp-   14 guide body-   15 second instrument, chisel-   17, 17′, 17″ base body-   19 rib-   21 contact position-   25 flattened area-   26 chamfer-   27 guide surface-   29 U or fork arm-   31 working web-   33 neck-   35 coupling section-   37 flat side-   39 coupling section-   41 counter surface-   α rib angle-   A shaft axis

1-23. (canceled) 24: A method of preparing a long bone for the receiptof a prosthesis, the prosthesis including an arcuate portion, the methodcomprising the steps of: inserting a guide body into a recess in thelong bone; positioning the guide body to correspond to an implantedposition of the prosthesis; and guiding an instrument along the guidebody and into the long bone, the instrument having an arcuate portioncorresponding to an arcuate portion of the prosthesis, the instrumentforming a recess in the long bone having the substantially same arcuateshape as the arcuate portion of the prosthesis. 25: The method of claim24, wherein the guiding step further comprises guiding an instrumentalong the guide body and into the long bone, the arcuate portion of theinstrument including an arcuate web extending outwardly therefrom, thearcuate web corresponding to an arcuate rib of the prosthesis, thearcuate rib of the prosthesis having a radius of curvature, wherein thearcuate web forms a recess in the long bone having the substantiallysame radius of curvature as the arcuate rib of the prosthesis. 26: Themethod of claim 24, further comprising the step of rasping the long boneto form a recess in the long bone. 27: The method of claim 24, whereinthe guiding step further comprises guiding an instrument along the guidebody by positioning at least a portion of the instrument within a recessformed in the guide body. 28: The method of claim 27, wherein theguiding step further comprises guiding a counter-surface of theinstrument along a guide surface of the guide body, wherein the guidesurface of the guide body defines the recess in the guide body. 29: Themethod of claim 24, wherein the guiding step further comprises guidingan instrument along the guide body by moving at least a portion of theinstrument along a track defined by the guide body. 30: The method ofclaim 24, wherein the instrument further comprises a substantiallyU-shaped instrument. 31: A method of preparing a femur for the receiptof a proximal femoral prosthesis, the prosthesis including an arcuaterib extending therefrom having a radius of curvature, the methodcomprising the steps of: rasping an intramedullary canal of the femur;inserting a guide body into the intrameduallary canal in the femur;positioning the guide body at least partially within the intrameduallarycanal, the position of the guide body corresponding to an implantedposition of the prosthesis; and guiding an instrument along the guidebody and at least partially into the intramedually canal of the femur,the instrument having an arcuate web extending outwardly therefrom, thearcuate web corresponding to the arcuate rib of the prosthesis, thearcuate web forming a track in the long bone having the substantiallysame radius of curvature as the arcuate rib of the prosthesis. 32: Themethod of claim 31, wherein the guiding step further comprises guidingan instrument along the guide body by positioning at least a portion ofthe instrument within a recess formed in the guide body. 33: The methodof claim 32, wherein the guiding step further comprises guiding acounter-surface of the instrument along a guide surface of the guidebody, wherein the guide surface of the guide body defines the recess inthe guide body. 34: The method of claim 31, wherein the guiding stepfurther comprises guiding an instrument along the guide body by guidingat least a portion of the instrument along a track defined by the guidebody. 35: The method of claim 31, wherein the instrument furthercomprises a substantially U-shaped instrument.